JP2902317B2 - Room temperature purification method and apparatus for inert gas - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to methane , carbon monoxide and nitrogen monoxide remaining in an inert gas such as a rare gas.
The present invention relates to a method for purifying an inert gas at room temperature, which efficiently removes a trace impurity component selected from the group under substantially room temperature conditions, and an apparatus therefor.

[0002]

2. Description of the Related Art Inert gases such as helium, neon, argon, krypton, xenon, and nitrogen used in many manufacturing processes often require high purity. Particularly in the semiconductor device manufacturing industry, an ultra-high purity inert gas is required, and the purity requirement is increasing year by year.

[0003] Against this background, commercially available industrial inert gas itself is also equipped with a pretreatment device for purifying the raw material air or increasing the number of rectification stages at ultra-low temperature. With the development, it is getting more and more purified.

Further, in a semiconductor wafer manufacturing process requiring higher purity, a special purifying device dedicated to the process is installed near the site so that a higher purity inert gas can be supplied. ing.

Japanese Patent Application Laid-Open No. 4-209710 discloses that a rare gas is mixed with a group VIII metal catalyst or a group Ib metal oxide in the range of 100-6.
After contacting at 00 ° C (preferably 300 to 500 ° C), an alloy getter containing zirconium as a main component and 300 ° C
A method for purifying a rare gas that removes nitrogen, hydrocarbons, carbon monoxide, carbon dioxide, oxygen, hydrogen, and water vapor contained as impurities in the rare gas by contacting at a temperature of preferably 400 to 700 ° C. It is shown. In this case, in the step of contacting the rare gas with the group VIII metal catalyst or the group Ib metal oxide on the upstream side, hydrocarbons such as methane are converted into hydrogen, moisture, carbon monoxide, carbon dioxide, and the like, and then, Impurities are captured and removed by reaction with the getter agent in the step of contacting with the downstream alloy getter.

Further, Japanese Patent Publication No. Hei 4-925 (JP-A-59-1985)
-116109), an argon gas is supplied at 150 to 300 ° C. in the presence of a trace amount of oxygen under a palladium catalyst.
First step of contacting at a temperature of 250-350 ° C
A second step of bringing into contact with a copper or nickel metal getter heated in the range of: a third step of bringing into contact with a 4A to 5A molecular sieve in a temperature range of room temperature or lower, and the argon gas after passing through the third step. A method for purifying argon gas comprising a fourth step of compressing at a temperature in the range of -10 to -50 ° C and 2 to 25 atm and passing through a molecular sieve having a mordenite crystal structure is shown. In this method, in the first step, the impurity components hydrogen and carbon monoxide are converted into carbon dioxide and moisture by the catalytic combustion power. In the second step, oxygen is adsorbed and removed. In the third step, carbon dioxide and moisture generated in the first step are adsorbed and removed. In the fourth step, nitrogen is adsorbed and removed.

Japanese Patent Application Laid-Open No. 4-293 filed by the present applicant
No. 514 discloses that an inert gas such as a rare gas containing a trace amount of hydrogen is mixed with a silver ion-exchanged zeolite which has been oxygen-coordinated in advance.
By contacting at 00 ° C. or lower (usually around room temperature), hydrogen in the inert gas is converted to moisture, and the generated water is immediately adsorbed on the zeolite to irreversibly reduce hydrogen to several ppb or less. The method is shown to remove them.

[0008]

As the degree of integration of semiconductors increases, the purity level required in the manufacture of VLSIs must be reduced to about 1 to 0.1 ppb or less for all impurity concentrations. Is being demanded.

However, even if the concentration of a specific impurity component can be reduced within the range of 10 to 1 ppb by a conventional general method, the total impurity component is always kept at about 1 to 0.1 ppb or less. It is difficult.

In the method described in JP-A-4-209710, a platinum-palladium catalyst or a copper oxide catalyst is used in the first stage of a two-stage reaction at a high temperature (400 ° C. in the example). It converts methane in gas to hydrogen, carbon monoxide, carbon dioxide, moisture, etc. The shift in this case is a shift based on a catalytic combustion reaction that consumes oxygen coexisting in the noble gas or the bound oxygen of the catalyst. Denatured carbon dioxide, moisture and residual impurities are trapped and removed by contacting at a high temperature (400 ° C. in the embodiment) as with the zirconium-based getter material provided in the second stage, It is said that impurity components in the rare gas are efficiently removed to a level of 10 ppb or less, and even 1 ppb or less.

Further, in the method for purifying argon gas described in Japanese Patent Publication No. 4-925, an argon gas is supplied in the presence of a trace amount of oxygen in the presence of a trace amount of oxygen under a palladium catalyst.
By contacting at a temperature of ° C., hydrogen and carbon monoxide as impurity components are converted into carbon dioxide and moisture, and the generated carbon dioxide and moisture are adsorbed and removed by a molecular sieve arranged at the subsequent stage. According to this method, when attention is paid to, for example, hydrogen and carbon monoxide, an argon gas containing 200 ppm of hydrogen and 100 ppm of carbon monoxide as impurity components is finally purified to an impurity component concentration of about 1 ppm ( See the examples in the publication).

However, Japanese Unexamined Patent Publication No.
No. 10 and Japanese Patent Publication No. 4-925, as the object of the present invention, use a gas such as a commercially available argon gas having a small content of an impurity component to be removed or a primary purified gas by a known method. , That is, the purity is 99.
9999-99.99999% (Total of residual impurities is 1000-100pp
If the target is an inert gas that has been highly purified by b), the cost of equipment such as a heater and the operating cost required for heating and the like become problems, and therefore, it cannot be said that the method is suitable for practical use.

[0013] The reason that it is not possible to always remove all impurity components to 1 ppb or less by these conventional methods is that in the conventional method, 100-600 ° C (preferably 30 ° C).
(0-500 ° C.) or 150-300 ° C., which causes side reactions, and the fact that heated desorbed gas from components causes recontamination. Conceivable.

In this respect, in the method disclosed in the above-mentioned Japanese Patent Application Laid-open No. Hei 4-293514 filed by the present applicant, an oxygen-coordinated silver ion-exchanged zeolite is used at room temperature, and a large amount of residual zeolite remains compared to other impure components. To reduce the amount of hydrogen irreversibly down to a few ppb or less, while removing other impurities such as methane, carbon monoxide and nitric oxide, and silver ions. The search for a catalyst species other than the exchanged zeolite was left as the next subject.

Under the above-mentioned circumstances, the present invention is intended to reduce the amount of various trace impurities remaining in an inert gas to an extremely low concentration of about 1 to 0.1 ppb or less under substantially room temperature conditions. It is an object of the present invention to provide a method and an apparatus for purifying an inert gas at room temperature, which can be effectively and stably removed up to.

[0016]

The method for purifying an inert gas at room temperature according to the present invention uses methane, carbon monoxide and nitric oxide.
The inert gas containing at least one trace impurity components selected from Li Cheng group was supported on an inorganic porous support, oxide
At least one selected from the group consisting of palladium and silver oxide
Both are characterized by removing trace impurity components contained in the inert gas by bringing them into contact with a kind of noble metal oxide catalyst under a temperature condition of 5 to 50 ° C.

The normal temperature purification unit of the inert gas of the present invention, main
Selected from the group consisting of tan, carbon monoxide and nitric oxide
A device for removing a trace impurity component from an inert gas containing at least one trace impurity component at a temperature of 5 to 50 ° C. , wherein a gas inlet (1) for introducing an inert gas containing a trace impurity component And an oxide powder supported on an inorganic porous carrier.
At least one selected from the group consisting of radium and silver oxide
Room temperature purification cylinder filled with a kind of noble metal oxide catalyst (2)
(3) and a gas outlet (5) through which the inert gas derived from the room temperature purification cylinder (3) is derived through a filter (4).

Hereinafter, the present invention will be described in detail.

Examples of the inert gas applicable to the method of the present invention include rare gases such as helium, neon, argon, krypton, and xenon, and nitrogen, and a mixed gas thereof.

The trace impurities contained in the inert gas include a group consisting of methane , carbon monoxide and nitric oxide .
At least one impurity component selected from the above, and even when all of these impurity components are included, even at room temperature, all the impurity components are reduced to about 1 to 0.1 ppb or to an extremely low concentration of less than about 1 ppb. The fact that it can be removed is also a feature of the present invention. It may contain methane , carbon monoxide, nitric oxide, as well as carbon dioxide and moisture. This is because carbon dioxide and moisture are removed by the inorganic porous carrier even under room temperature conditions.

[0021] as the noble metal oxide catalyst, at least one <br/> the like selected from the group consisting of palladium oxide and silver oxide. Oxidative palladium and silver oxide, the temperature for generating the oxide can be relatively low temperatures and gas phase oxidation with 200 to 600 ° C., often catalytic function reproducing operation be adopted as conventional means after impurity components removed This is because it can be easily implemented.

The above-mentioned noble metal oxide catalyst includes PdO, Ag
It is not essential that the oxides have stoichiometric ratios such as O and Ag ₂ O, and oxides in a state of oxygen deficiency, for example, PdO
_{Even 1-x} , AgO _1-x , and Ag ₂ O _1-x (0 <X <0.5) exhibit a sufficient function for the purpose of the present invention to remove trace impurities.

The above-mentioned noble metal catalyst which is not in an oxide state even though it is a noble metal does not undergo any methane chemisorption reaction at room temperature, and is not suitable for the purpose of the present invention (see Comparative Examples 1 and 2 described later). (See FIG. 4).

Examples of the inorganic porous carrier for supporting the above-mentioned noble metal oxide catalyst include those having a catalyst-supporting ability and an ability to adsorb carbon dioxide and moisture.
For example, alumina, silica / alumina, molecular sieves and the like are preferably used.

The loading amount of the noble metal oxide catalyst on the inorganic porous carrier is preferably about 0.1 to 20% by weight, particularly preferably 0.5 to 15% by weight. When the supported amount is too small, the removal of methane , carbon monoxide, and nitric oxide is not sufficiently performed. On the other hand, when the supported amount is too large, it becomes difficult to uniformly support the catalyst and the catalyst price increases. It becomes uneconomical.

In order to support a noble metal oxide catalyst on an inorganic porous carrier, an aqueous solution of a salt or a complex ion of a noble metal is supported on the inorganic porous carrier, and then heat-treated in an oxidizing atmosphere such as in air or oxygen. I just need. The heating and oxidizing conditions vary depending on the type of carrier, the amount of the carrier, and the type of oxidizing atmosphere. The above-mentioned heating and oxidizing operation may be performed by using a room-temperature refining cylinder (3) described later. After performing the operation of removing trace impurities according to the present invention, the room temperature purification cylinder
It is also possible to regenerate the catalyst in an oxidizing atmosphere in (3).

The contact of the inert gas containing a trace amount of impurity components were supported on an inorganic porous support and a noble metal oxide catalyst, 5
５０50 ° C., in other words, at room temperature conditions in which substantially no external heating or cooling is performed. Contact temperature is 50
Above ℃ , the adsorbed impurities tend to desorb again
If the temperature is further increased, the adsorbed impurity components may be converted into CO ₂ .

The purifying apparatus for carrying out the above method includes: a gas inlet for introducing an inert gas containing a trace impurity component;
(1) and a noble metal oxide catalyst supported on an inorganic porous carrier (2)
A room temperature purifying cylinder (3) filled with: and a gas outlet (5) for drawing out an inert gas derived from the room temperature purifying cylinder (3) through a filter (4) are preferably used. . Two room temperature refining cylinders (3) may be provided in parallel, and while one is being purified by flowing an inert gas, the other may be regenerated or replaced.

[0029]

[Action] Inert gas containing trace impurities is supplied to gas inlet (1)
From the noble metal oxide catalyst (2) supported on the inorganic porous support and contacting the catalyst at a temperature of 5 to 50 ° C. in the room-temperature purification column (2) to oxidize the noble metal supported on the inorganic porous support. All of the impurity components, methane , carbon monoxide and nitrogen monoxide, are removed to about 1 to 0.1 ppb or less by the chemical adsorption action of the product catalyst. The inert gas from which the impurity components have been removed in this way passes through the filter (4) and passes through the gas outlet.
Removed from (5) and used for the intended purpose.

According to the present invention, methane remaining in the inert gas, or carbon monoxide and nitric oxide
A small amount of the selected impurity component is added under a substantially room temperature condition with a small amount of a filler relative to the flow rate of the inert gas.
It can be effectively and stably removed to an extremely low concentration of about 0.1 ppb or less.

Even if a small amount of carbon dioxide or moisture is contained in the inert gas, they are physically adsorbed to the inorganic porous carrier and removed.

The mechanism by which methane , carbon monoxide, and nitrogen monoxide , which are trace impurities in the inert gas, are removed at about room temperature by contact with the noble metal oxide catalyst, adsorbs these impurities as molecules. It is considered to be normal temperature chemisorption. That is, by oxygen is bonded to the noble metal catalyst [Pd ⁺ O ^-] and the like of the positive ionization negative occurs, methane is polarized by each charged moiety is at room temperature range, carbon monoxide,
It is considered that these impurities are efficiently removed as a result of the chemical adsorption of the nitric oxide by being electrically sucked. These impurities cannot be removed because the inorganic porous carrier alone is practically hardly physically adsorbed by itself. Carbon dioxide and water, which are other impure components, are easily removed by the room temperature physical adsorption action of the inorganic porous carrier used as the carrier.

The above-described mechanism is described in Embodiment 1 and FIG.
This is supported by the experimental facts at. In other words, taking methane as an example, the spent noble metal oxide catalyst (palladium oxide catalyst) after performing the impurity component (methane) load test at room temperature is replaced with an inert gas containing no impurity component (methane). 200 ° C from room temperature while flowing (pure argon)
When the heated gas was analyzed, the methane removed near room temperature was only chemisorbed on the surface of the palladium oxide as methane molecules ( for example, when the temperature exceeded 60 ° C., methane began to be desorbed). , Below 100 ° C
_It can be seen that the oxidizing effect of palladium oxide is not exhibited at around 130 ° C. without being oxidized to ₂ . As described above, the mechanism for removing impurity components according to the present invention is described in Japanese Patent Application Laid-Open No. 4-209710 and Japanese Patent Publication No.
No. 5 mechanism, that is, 100 to 600 ° C.
A mechanism that transforms hydrocarbons such as methane into hydrogen, moisture, carbon monoxide, carbon dioxide, etc. by coexisting oxygen or catalytic combustion reaction under high temperature conditions (preferably 300 to 500 ° C.), or a high temperature of 150 to 300 ° C. The mechanism for converting hydrogen or carbon monoxide into carbon dioxide and moisture by catalytic combustion under conditions is fundamentally different.

[0034]

The present invention will be further described with reference to the following examples.

Example 1 FIG. 1 is a diagram showing an apparatus for purifying an inert gas at room temperature used in Example 1, and also shows a system for quantitatively adding an impurity to an inert gas and a sample gas analysis system. is there.

In the apparatus of FIG. 1, (A) is a system for quantitatively adding impurity components, (B) is a room temperature purification device, and (C) is a sample gas analysis system. The system (A) for quantitatively adding an impurity component includes an inert gas supply source (6) and an impurity component supply source (7). The room temperature purification device (B) includes a gas inlet (1), a noble metal oxide catalyst (2) supported on an inorganic porous carrier, a room temperature purification cylinder (3), and a filter (4).
And a gas outlet (5). Sample gas analysis system (C)
The apparatus includes a purified gas outlet (8), a gas chromatograph (9), an atmospheric pressure ionization mass spectrometer (10), and a sample gas outlet (11). In FIG. 1 (and FIG. 5 described later),
(MC) is a mass flow controller, (MF) is a mass flow meter, (V) is a valve, and (NV) is a needle valve.

Using the apparatus shown in FIG. 1, an experiment for removing trace impurities in the inert gas was performed as follows.

8% by weight of palladium oxide supported on spherical alumina having a diameter of 2 mmφ (a commercially available product in which a palladium catalyst is supported on alumina is obtained at 500 ° C. in air at 3 ° C.).
Heat-oxidized) for SUS-
A 316L room temperature purification cylinder (3) was filled to a height of 88 mm.

Methane was added at a fixed amount of 380 ppb to pure argon gas purified by a known ultra-low temperature adsorption method in advance to obtain a supply gas. This gas is introduced through the gas inlet (1),
A room temperature purification column (3) is passed through GHSV2400h ^-1 at room temperature, and a filter (4) (filtration accuracy) installed for the purpose of removing particles (fine particles) as solid impurities
(All metal filter with 0.01μm sintered metal filter media and SUS-316L housing)
Through the gas outlet (5). The analysis of methane in the purified argon gas is performed by an atmospheric pressure ionization mass spectrometer (model: UG-240A P / N, manufactured by Hitachi, Ltd.).
This was performed using (10).

FIG. 2 is a graph showing the result of an experiment for removing trace impurities in the inert gas in Example 1. As shown in FIG. 2, 3
80 ppb of methane was removed to less than 0.05 ppb (limit of quantification) and the removal lasted 76 hours.

It is to be noted that the argon gas from the system (A) for quantitatively adding the impure component (methane) may contain trace amounts of carbon monoxide, carbon dioxide, oxygen, hydrogen and nitrogen monoxide. However, within 76 hours after the start of the purification, the concentration of each of these components in the purified argon gas remained below the limit of quantification (there was no change showing an increasing trend), indicating that there were no by-product compounds. I was

FIG. 3 is a graph showing the analysis results of desorbed gas when the temperature of the used catalyst after removing trace impurities in the inert gas at room temperature was raised.

Next, the used palladium oxide catalyst subjected to the methane load test under room temperature conditions as described above was heated from room temperature to 200 ° C. while flowing the purified methane-free argon. The heated gas was analyzed. The results are as shown in FIG. 3. The methane removed near room temperature is chemically adsorbed on the surface of palladium oxide as methane molecules, and after the temperature rise exceeds 60 ° C., desorption of methane starts and 140 ° C. starts. Continued to near. The adsorbed methane is not oxidized to CO ₂ below 100 ° C.
The oxidizing effect of palladium oxide is expressed at 130 ° C
Was over.

Comparative Example 1 Example 1 was repeated, except that a palladium oxide was replaced with a palladium metal catalyst by a reduction treatment, and the other conditions were the same as in Example 1.

FIG. 4 is a graph showing the results of an experiment for removing trace impurities in the inert gas in Comparative Example 1, and the results of Example 1 are additionally shown. As shown in FIG. 4, immediately after the gas was supplied to the room temperature purification cylinder (3),
The methane concentration in the gas discharged from the gas outlet (5) sharply increased, and after 8 minutes (one scan time), reached 378 ppb, which was almost the same as the methane concentration in the supply gas, and became a uniform value. This fact indicates that metal palladium is not suitable for chemisorbing methane in the room temperature range, and that palladium oxide must be used.

Example 2 FIG. 5 is a diagram showing an apparatus for purifying an inert gas at room temperature used in Example 2, with a system for quantitatively adding an impurity component to the inert gas and a sample gas analysis system additionally shown. is there.

The outline of the apparatus is the same as that of the first embodiment shown in FIG. 1, except that a methane supply source (7a), a carbon monoxide supply source (7b), and a nitric oxide supply are used as impurity component supply sources (7). Source (7c)
The filter (4) is provided outside the room temperature purification column (3).

In order to remove trace impurities in the inert gas, an experiment for removing trace impurities in the inert gas was conducted using the apparatus shown in FIG.

10% by weight of silver oxide supported on spherical silica-alumina having a diameter of 2 mmφ was prepared by using SU having an inner diameter of 23 mm.
An S-316L room temperature purification cylinder (3) was filled to a height of 46 mm.

Pure helium gas purified by a known ultra-low temperature adsorption method is supplied with 50 ppb of methane and 50 ppb of carbon monoxide.
And 50 ppb of nitrogen monoxide were added in fixed amounts to form a supply gas. This gas was introduced from the gas inlet (1), passed through a room temperature purification column (1) at room temperature under GHSV 2400 h ^-1 , and After passing through the same type of filter (4) as in the case (1), the gas was led out from the gas outlet (5). The analysis of methane, carbon monoxide, and nitric oxide in the purified helium gas was performed using the same atmospheric pressure ionization mass spectrometer (10) as in Example 1. The results are as shown in Table 1. The concentrations of methane, carbon monoxide and nitric oxide in the purified gas were all less than the quantification limit of 0.05 ppb or 0.1 ppb.

[0051]

[Table 1]  Impurity components Transit time Concentration before purification Concentration after purification  Methane (CH_Four) 400hr 50ppb 0.05ppb or less Carbon monoxide (CO) 400hr 50ppb 0.05ppb or lessNitric oxide (NO) 400hr 50ppb 0.1ppb or less

[0052]

According to the present invention, there is selected from methane , carbon monoxide and nitric oxide remaining in the inert gas.
To effectively and stably remove trace impurity components to an extremely low concentration of about 1 to 0.1 ppb or less under a room temperature condition with a small amount of a filler relative to the flow rate of the inert gas. Can be.

Therefore, the present invention is extremely useful as an industrial method and apparatus for removing a trace amount of impurities remaining in an inert gas.

[Brief description of the drawings]

FIG. 1 is a diagram showing an apparatus for purifying an inert gas at room temperature used in Example 1, in which a system for quantitatively adding an impurity to an inert gas and a system for analyzing a sample gas are additionally shown.

FIG. 2 is a graph showing the results of an experiment for removing trace impurities in an inert gas in Example 1.

FIG. 3 is a graph showing an analysis result of desorbed gas when the temperature of a used catalyst after removing trace impurities in an inert gas under a room temperature condition is raised.

FIG. 4 is a graph showing a result of an experiment for removing a trace impurity component in an inert gas in Comparative Example 1, in which the result of Example 1 is additionally shown.

FIG. 5 is an apparatus diagram showing an apparatus for purifying an inert gas at room temperature used in Example 2, in which a system for quantitatively adding an impurity to the inert gas and a sample gas analysis system are additionally shown.

[Explanation of symbols]

(1) ... gas inlet, (2) ... noble metal oxide catalyst supported on inorganic porous carrier, (3) ... room temperature purification cylinder, (4) ... filter,
(5) ... gas outlet, (6) ... inert gas supply source, (7) ... impurity component supply source, (7a) ... methane supply source, (7b) ... carbon monoxide supply source, (7c) ... monoxide Nitrogen supply source, (8)… purified gas outlet,
(9) ... gas chromatograph, (10) ... atmospheric pressure ionization mass spectrometer, (11) ... sample gas outlet, (A) ... quantitative addition system of impure components, (B) ... room temperature purification equipment, (C) ... sample Gas analysis system, (MC) Mass flow controller, (MF) Mass flow meter, (V) Valve, (NV) Needle valve

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B01D 53/86 B01J 23/44 B01J 23/50

Claims (2)

(57) [Claims] 1. A method according to claim 1, wherein methane, carbon monoxide and nitric oxide are used.
Comprising an inert gas containing at least one trace impurity components selected from the group, it was supported on an inorganic porous support, oxidized Pas
At least one selected from the group consisting of radium and silver oxide
A method for purifying an inert gas at room temperature, comprising removing a trace impurity component contained in the inert gas by contacting the same with a kind of noble metal oxide catalyst under a temperature condition of 5 to 50 ° C. . 2. From methane, carbon monoxide and nitric oxide
An apparatus for removing a trace impurity component from an inert gas containing at least one trace impurity component selected from the group under the temperature condition of 5 to 50 ° C. , wherein the gas introducing the trace gas-containing inert gas is provided. An inlet (1) and a member selected from the group consisting of palladium oxide and silver oxide supported on an inorganic porous carrier.
A normal temperature purification column (3) filled with at least one noble metal oxide catalyst (2) separated, and a gas outlet through which an inert gas derived from the normal temperature purification column (3) passes through a filter (4).
(5) An inert gas purifying apparatus at normal temperature, comprising: